Impact of cyclone Ockhi on phytoplankton size classes structure in the Arabian Sea

ABSTRACT

Short-term events like tropical cyclones often have a strong impact on the upper ocean, causing transient changes in the physical and chemical properties of the sea. These changes could potentially affect the distribution pattern of the phytoplankton community. The present study aims to investigate the impact of the distribution of phytoplankton size classes (PSCs) caused by the tropical cyclonic event Ockhi in the Arabian Sea (AS) in 2017. Multiple datasets, including satellite remote sensing and reanalysis data, were utilized to observe the biogeochemical variability and the corresponding changes in PSCs distribution caused by the Ockhi cyclone event. One of the predominant issues in using satellite remote sensing data is the loss of data due to overcast conditions, which was resolved by reconstructing the chl-a and SST using an empirical orthogonal function. The results show a short-term shift in the PSCs pattern from the pico and nano-rich region to the micro-dominated environment in the cyclone passage region during the post-cyclone period. When comparing the results with the physical and biochemical parameters, it was found that the cyclonic event triggered the deep-seated nutrients to the surface, which promoted favourable conditions for microorganisms to proliferate for a short span in the cyclone passage region. The overall study highlights the impact of the Ockhi cyclone on biogeochemical changes and corresponding shifts in the phytoplankton size distribution along the cyclone path.

KEYWORDS:

• Phytoplankton size classes
• tropical cyclone
• remote sensing
• gap-filling
• Arabian Sea

Acknowledgements

The authors would like to thank NASA for the open-source chlorophyll-a concentration and SST data and CMEMS for the MLD, salinity, and nutrient data. The authors would also like to thank the Department of Science and Technology for supporting this research through the DST-INSPIRE fellowship programme under the Grant no: IF170191. The authors thank the editor and anonymous reviewers, whose suggestions greatly improved this work.

Disclosure statement

No potential conflict of interest was reported by the author(s).